The specific timing of Fallon’s ascent was still unclear, but sources said he would take over on the heels of the Olympics coverage, which runs Feb. 7-23. A source said he’d be behind the “Tonight” desk by early March at the latest.

Today was one of the most exciting days of my life. I read every tweet and every post and I thank you.

The announcement comes after weeks of rumors and on-air carping from Leno about the network’s handling of the “Tonight Show” handoff. Burke flew to Los Angeles on March 24 to come to terms with Leno and smooth the way for “Late Night” host Fallon to move up to 11:35 p.m. In a sign that a deal was coming together, however, Leno and Fallon poked fun at the situation on Monday night with a seg that ran as a bridge between the two programs.

NBC’s formal announcement of the transition was accelerated by the burst of media speculation about Fallon’s promotion. NBC sources said that Burke had always seen Fallon as the logical successor to Leno, even before ABC moved “Jimmy Kimmel Live” up to the 11:35 p.m. slot. After the rumors went into overdrive, Burke’s focus turned allowing Leno to set his own exit terms, to a degree. It was understood within NBC that the two-year contract Leno set in 2012 would be his last on “Tonight.”

Hanging over the Leno-Fallon transition is still the dark cloud of the Peacock’s last “Tonight Show” transition in 2009-2010, which ended disastrously when Conan O’Brien was ousted after only eight months at the helm. And Leno’s reputation took a beating when he returned to the “Tonight” desk after flopping with a 10 p.m. nightly variety show on NBC. O’Brien ultimately moved on to his latenight perch at TBS, after securing a whopping $45 million payout.

In the March 24 meeting in Leno’s office in Burbank, Burke laid out multiple scenarios for Leno’s final bow on the show, including having him stay through the end of his contract in September 2014. The two came to the conclusion that making the switch on the heels of what is sure to be 17 nights of highly rated Olympics coverage in February would be ideal for Fallon.

According to a source, Leno was impressed by Burke’s outreach, and noted in the meeting that he had not been consulted on the 2009 shuffle — a timetable laid out five years earlier in a contract negotiation between O’Brien and NBC.

The formal news of Fallon’s pending promotion will shift speculation to what NBC plans to do with the 12:35 a.m. hour that is now home to “Late Night.” “Saturday Night Live” vet Seth Meyers has been mentioned as a strong candidate to take over the show, but Peacock sources say plans for that hour are still very much in development — indicating that there may be a broader shift under way beyond finding a new host. The plan for the “Late Night” hour will be hammered out by the time NBC hosts its upfront on May 13.

In announcing the transition on Wednesday, NBC sought to put a comedic spin on Leno’s retirement after 22 years (with an eight-month gap) on the show.

Said Leno: “Congratulations Jimmy. I hope you’re as lucky as me and hold on to the job until you’re the old guy. If you need me, I’ll be at the garage.”

Said Fallon: “I’m really excited to host a show that starts today instead of tomorrow.”

With Fallon taking over, “The Tonight Show” will shift back to Gotham for the first time since Johnny Carson relocated NBC staple to Burbank in 1972. Lorne Michaels, exec producer of “Late Night” and a champion of Fallon since his “Saturday Night Live” days, will shift to “Tonight” with Fallon.

NBC’s decision to make the change on “Tonight” sooner rather than later surprised industry observers, given that Leno had retained his No. 1 ranking in the competitive timeslot against all odds — and the weakness of NBC’s primetime lineup. The move was seen as being spurred by ABC’s upgrade of Jimmy Kimmel to the 11:35 slot in January, and concern that ABC would beachhead in the slot with younger viewers if NBC didn’t move quickly. However, NBC sources insisted that the Fallon plan was in the works long before Kimmel’s move.

“We are purposefully making this change when Jay is No. 1, just as Jay replaced Johnny Carson when he was No. 1. Jimmy Fallon is a unique talent and this is his time. I’m thrilled he will become the sixth host of ‘The Tonight Show’ at exactly the right moment, in conjunction with our coverage of next year’s Winter Olympic Games from Sochi, Russia,” Burke said.

Another winner in the “Tonight Show” shuffle is New York City. Gotham mayor Michael Bloomberg was quick to crow about reclaiming the kingpin show of latenight.

“It’s the perfect symbol of incredible comeback we’ve worked to create in our city’s film and television industry,” Bloomberg said in a statement. ” Not since the since the invention of television has so much production been based in our city, which is creating good-paying jobs for New Yorkers in all five boroughs. Today, more than 130,000 New Yorkers make their living working behind the scenes on productions – a 30 percent increase over the past decade, and the numbers continue to grow. ‘The Tonight Show’ will bring even more jobs and economic activity to our city – and we couldn’t be happier that one of New York’s own is bringing the show back to where it started – and where it belongs.”